1. Field of the Invention
This invention relates to a system for discharging material from a vehicle and, more particularly, to a conveyor arrangement mounted to a vehicle, such as a truck. The vehicle has a material holding container connected to one or more hoppers leading to an endless belt transporter arrangement situated directly underneath the material holding container.
2. Description of the Prior Art
The material for discharge is any divided material such as gravel or sand. It is desirable to deposit the material at a location remote from the immediate area around the vehicle, thus an apparatus as disclosed in U.S. Pat. No. 5,286,158 has been developed. The discharged material is flung at high speed from the apparatus, directed towards the deposit area. The discharge apparatus includes a high speed endless belt having a lower middle cross-section and higher sides, to keep the material centred on the belt. Above the belt, a constraining member which deflects material to be distributed onto the central portion of the belt and also retains the material on this central portion. The constraining member is basically a deflector shield to prevent material from leaving the belt before the material reaches the discharge opening. The constant barrage of loose material on the constraining member creates an unnecessary high noise level at the same time as the wear on the constraining member is unnecessary high. At the same time, the material is accelerated up to discharge speed only by the gravitational and frictional forces working on and between the first belt and the material.
Today, the most commonly used vehicle has a material holding container mounted on the vehicle, a plurality of material feeding means arranged at a lower part of the container, and a first material transport means arranged to transport material from the feeding means. The material transport means is usually a low speed first endless belt running over a plurality of first rollers. The first endless belt has a first end, located adjacent the material holding container, and a second end, located away from the material holding container. A second material transport means is arranged to cooperate with the first material transport means and this second material transport means is usually a second endless belt running over a plurality of second rollers. The second endless belt has a third end, located adjacent the second end of the first endless belt, and a fourth end, pointing in the direction of the desired material discharge. The second material transport means further has a material hold-down means arranged above the material transport means and in frictional contact with the second endless belt. The material hold-down means is usually a third endless belt. This third endless belt is driven by frictional forces between itself and the second endless belt, and usually has a forward roller, a rearward roller and downwardly arranged pulley wheels to keep the third endless belt stretched along a distance of the second endless belt, so that the material is securely held between the two belts to prevent any material from leaving the second endless belt before the material has reached the desired discharge speed. Large tracking problems are often associated with this construction of the third endless belt, i.e. the belt does not stay centred on the rollers, but tries to leave the rollers in either sideways direction. To combat this, end wheels or flanged ends of the rollers have been used, which forcibly constrain the belt to remain on the rollers. This increases the power required to propel the second endless belt because of the increased power lost to frictional forces, and also increases the wear and tear on the third endless belt.
There is a need for an improved apparatus which would provide for less required driving power for the second endless belt and lower wear on the third endless belt.